This invention relates to a refractory composition containing a basic refractory material and suitable for preparing refractories.
In the art of steel making, the open hearth process and the bottom-blown converter process have been gradually substituted by the pure oxygen top-blown converter process due to the development of the latter. With an extensive increase in the production quantity of crude steel, the demand for basic refractories has also been increased greatly, with the result that the demand for dolomite clinker and dolomite magnesia clinker which are used as the raw materials for preparing basic refractories in such converter furnaces has also been increased. For this reason, it is a recent trend that acidic refractories are substituted by basic refractories in most cases.
When molding refractories, where the binding force of the raw material refractory substance itself is low, various types of binders are added. Silica sol is an excellent binder. When silica sol is used as a binder it is possible to obtain excellent refractories owing to its strong bonding force manifested by it at the time of hardening and the refractive property of silica. Where a basic refractory raw material, for example magnesia clinker, is mixed with silica sol for molding basic refractories, the silica sol almost instantly gels so that it is difficult to obtain molded products of high mechanical strength. Even when molded under a high pressure and subsequently dried or fired, the mechanical strength of the dried or fired molded products is extrememly low because the bonding force of the silica sol has not been manifested. For this reason, it has been generally recognized that use of silica sol is not effective for the raw material of basic refractories.
Water glass such as potassium-, sodium-, lithium-silicate, etc. has also been used as the binder for basic refractories. However, since water glass contains a large quantity of alkali metals, molded refractories using water glass are difficult to sufficiently dry and have a high tendency toward deliquescence and slaking. Moreover, the refractoriness of such molded articles is low. For this reason, the field of application of the refractories using water glass is limited.
It has been proposed to use guanidine silicate as a silica type binder as disclosed in the specification of Japanese patent publication No. 128 of 1970. However, not only is the supply source of guanidine silicate limited as an industrial material, but also the mechanical strength of basic refractories using this binder is not so high.
Magnesium chloride, tar etc. are also used as the binder for basic refractories, but the mechanical strength after drying of basic refractory raw material using such binders is low so that sufficiently high mechanical strength can not be attained unless the molded articles are fired. Where tar is used, it has been recognized that the mechanical strength decreases unexpectedly when the molded articles are fired at a temperature of about 800.degree.C. Where magnesium cloride is used the molded refractories have a tendency toward deliquescence and slaking.
Accordingly, it will be highly valued to obtain refractories having a high mechanical strength and not manifesting the properties of deliquescence and slaking by using a silica type binder for basic refractory raw materials.